A cyclopentene ring-opening polymer which is obtained by metathesis ring-opening polymerization of cyclopentene is widely known as a rubber material and is used as a rubber material which is blended with carbon black, silica, and other inorganic particles. In general, a cyclopentene ring-opening polymer, for example, as disclosed in Patent Document 1, is produced using a so-called Ziegler-Natta catalyst, which is comprised of WCl6, MoCl5, or other transition metal compound of Group VI of the Periodic Table and an aluminum compound, tin compound, or other organometallic compound, by bulk polymerization or solution polymerization. In some cases, a molecular weight adjuster constituted by a-olefin is added. The thus obtained cyclopentene ring-opening polymer is comprised of only carbon atoms and hydrogen atoms, so the affinity with carbon black, silica, and other inorganic particles is low. For this reason, even if blending inorganic particles into such a cyclopentene ring-opening polymer to form a composition, the effect of inorganic particles in improving the mechanical properties cannot be sufficiently exhibited.
As a technique for improving the affinity of a cyclopentene ring-opening polymer with inorganic particles, in Patent Document 2, a method is proposed of using a ruthenium-carbene complex as a catalyst in the presence of a compound which has functional groups and ethylenically unsaturated bonds (for example, allyltrimethoxysilane etc.) so as to polymerize cyclopentene by ring-opening polymerization and use the metathesis reaction between the polymer chain terminal ends of cyclopentene ring-opening polymer and the ethylenically unsaturated bonds to introduce functional groups to the terminal ends of the cyclopentene ring-opening polymer. The cyclopentene ring-opening polymer which has functional groups at the terminal ends which is obtained by this method is greatly improved in affinity with inorganic particles compared with one which does not have functional groups.
However, if considering the rising demand for low fuel consumption performance from tires in recent years, when using a cyclopentene ring-opening polymer as a composition for tire applications, even the cyclopentene ring-opening polymer which is obtained by the method which is described in Patent Document 2 will hopefully be improved in low heat generation property. For example, even if introducing an alkoxysilyl group, which is considered to have excellent performance as a functional group which is introduced for improving the affinity with inorganic particles for styrene-butadiene rubber etc. which are being broadly used currently for tire applications, into the cyclopentene ring-opening polymer by the method of Patent Document 2, there is still room for improvement of the low heat generation property in the thus obtained polymer composition.